1. Field of the Invention
This invention pertains to the field of urethane catalysts. More particularly, this invention relates to the use of certain dimethylamino polyalkyleneoxy isopropanols as catalysts for preparing polyurethane foam.
2. Description of Related Art
The use of a catalyst when preparing polyurethanes by reacting a polyisocyanate with an active hydrogen-containing compound, as measured by the Zerewitinoff method, such as a polyol, and other optional ingredients, is known. Catalysts are employed to promote at least two, and generally three, major reactions. These reactions must proceed simultaneously and at competitively balanced rates during the process in order to yield a polyurethane with desired physical characteristics.
One reaction is a chain extending isocyanate-hydroxyl reaction by which a hydroxyl-containing molecule is reacted with an isocyanate-containing molecule to form the urethane. The progress of this reaction increases the viscosity of the mixture and forms a polyurethane containing a secondary nitrogen atom in the urethane groups.
A second reaction is a cross-linking isocyanate-urethane reaction wherein an isocyanate-containing molecule reacts with the secondary nitrogen atom of the urethane group. The third reaction, which often is important, particularly when the preparation of flexible polyurethane foam is desired, comprises an isocyanate-water reaction wherein an isocyanate-terminated molecule is extended and by which carbon dioxide is generated to "blow" or assist in the "blowing" of the foam. The in-situ generation of carbon dioxide by this reaction plays an essential part in the preparation of "one-shot" flexible polyurethane foams.
In order to obtain a good urethane foam structure, these reactions must proceed simultaneously at optimum balanced rates relative to each other. For example, if the carbon dioxide evolution is too rapid in comparison with the chain extension reaction, the foam tends to collapse. Alternatively, if the chain extension reaction is too rapid in comparison with the reaction that generates carbon dioxide, foam rise will be restricted, thus resulting in a high-density foam with a high percentage of poorly defined cells. Finally, if crosslinking reactions, including the second reaction, do not keep pace with the first or third reactions, the foam may not be stable because of the absence of adequate cross-linking.
It has long been known that tertiary amines, such as trimethylamine, triethylamine, tetramethylpropanediamine, triethy lenediamine, dimethylethanolamine, methyltriethylenediamine, N-methylmorpholine, N-ethylmorpholine and the like are effective for catalyzing the cross-linking isocyanate-urethane reaction. Many of the tertiary amines also are effective for catalyzing the water-isocyanate reaction that causes carbon dioxide evolution. A variety of tertiary amine catalysts are disclosed in U.S. Pat. Nos. 3,476,933, 3,925,268, 3,127,436 and 3,243,389.
However, tertiary amines are only partially effective as catalysts for the chain extension reaction and thus normally are used in combination with other catalysts, typically an organic tin catalyst. For example, in the preparation of flexible foams, a one-step or "one-shot" process has long been used wherein triethylenediamine is employed for promoting the water-isocyanate reaction and the crosslinking reaction; while an organic tin compound is used in synergistic combination with the triethylenediamine to promote the chain extension reaction.
One problem with triethylenediamine and other similar materials is that they are solids and must be dissolved prior to use to avoid processing difficulties such as non-homogeneous reactions. Also, triethylenediamine and many of the other prior art amines impart a strong amine odor to the polyurethane foam. In addition to odor and handling problems, certain other tertiary amines are very high in relative volatility and present significant safety and toxicity problems.
U.S. Pat. No. 2,941,967 discloses a process for catalytically enhancing the reaction of an isocyanate with a polyol by including mono and diamino ethers, e.g., dimethyl-(2-methoxyethyl)-amine and bis-(3-dimethylaminopropyl)ether as a catalytic component.
U.S. Pat. Nos. 3,330,782 and 3,480,675 disclose using tertiary amine ethers as catalysts for the reaction of organic polyisocyanates with active hydrogen-containing compounds. In the '782 patent, beta-(N,N-dimethylamino) alkyl ethers are used as catalysts for the urethane reaction.
U.S. Pat. No. 3,622,542 and U.S. Pat. No. 4,495,081 disclose using N,N'-tetramethyl-2-hydroxy-1,3-diaminopropane as a catalyst for preparing polyurethane foams.
U.S. Pat. No. 3,632,707 uses a mixture of trimethylaminoethylpiperazine and dimethylamino ethanol as a catalyst for preparing flexible polyurethane foam from a polyether polyol using the "one shot" process.
U.S. Pat. No. 3,645,925 discloses an amine catalyst for a polyurethane reaction consisting of a 4,4'-dimorpholinodiethyl ether. Its use in combination with other tertiary amines also is disclosed.
U.S. Pat. No. 3,786,029 describes using amino-orthoesters, prepared by reacting amino alkanols, such as 1-methyl-2-(N,N-dimethylaminoethoxy) ethanol, with an orthoester, as catalysts for polyurethane formation.
U.S. Pat. Nos. 4,410,466 and 4,101,470 describe certain bis(dimethylaminopropyl)-amine derivatives which include ethers and alcohol-terminated compounds. These components are alleged to have catalytic activity for urethane synthesis.
U.S. Pat. Nos. 4,419,461 and 4,421,869 disclose using the combination (i.e. a partial salt) of 3-dimethylaminopropylamine and either a branched octanoic acid or phenol as a catalyst for preparing polyurethane foam.
U.S. Pat. No. 4,582,938 also relates to certain bis(dialkylaminoethyl) polyamine ethers useful as catalysts for urethane synthesis.
Included among the above catalysts useful for urethane synthesis are tertiary amines having active hydrogens, which thus are reactive with isocyanate groups. Such tertiary amines include triethanolamine; triisopropanolamine; N-methyldiethanolamine; N-ethyldiethanolamine; N,N-dimethylethanolamine and their reaction products with alkylene oxides such as propylene oxide and/or ethylene oxide. See, for example, U.S. Pat. Nos. 3,669,913; 3,793,237; 4,190,417 and 4,304,872.
Polyamines also have been used as the active hydrogen-containing reactant for preparing polyurethanes. U.S. Pat. No. 2,697,118 describes using N,N,N',N'-tetrakis-(2-hydroxypropyl)-ethylene diamine. U.S. Pat. No. 3,697,458 uses the propoxylated adduct of the reaction product of a dialkanolamine and an epihalohydrin. U.S. Pat. No. 3,330,782 discloses using the alkylene oxide adducts of trialkanolamines. U.S. Pat. No. 3,847,992 uses partially aminated polyoxyalkylene polyols containing primary hydroxyl groups and possibly some terminal secondary hydroxyl groups. See also U.S. Pat. Nos. 3,125,540; 3,383,351 and 3,404,105 and G.B. Patent No. 1,028,810.